1. Field of the Invention
The present invention relates to an angular-velocity detection apparatus which is suitably used to detect an angular velocity applied to, for example, a rotation member. More particularly, this invention provides an angular-velocity detection apparatus comprising a substrate, a vibrating body provided on the substrate, the vibrating body being capable of displacing in a vibration axis direction and a detection axis direction which intersect at right angles to each other, vibration generation means for vibrating the vibrating body in the vibration axis direction by applying a driving signal, and displacement detection means for detecting the amount of displacement of the vibrating body when the vibrating body is displaced in the detection axis direction on the basis of the angular velocity along a detected axis intersecting at right angles to the vibration axis and the detection axis in a state of the vibrating body being vibrated in the vibration axis direction by the vibration generation means.
2. Description of the Related Art
Generally, in angular-velocity detection apparatus, when a rotational force is applied about a Z axis which serves as a detected axis in a state in which a vibrating body is vibrated in the direction of a vibration axis in the three axes of X, Y and Z axes, a Coriolis force (inertial force) acts on the vibrating body, causing the vibrating body to vibrate in the direction of the Y axis which serves as a detection axis. Angular velocity detection apparatus which detect the displacement of the vibrating body in the direction of the Y axis due to this Coriolis force as an electrical charge generated in a piezoelectric member or as a change in a voltage, electrostatic capacitance or the like. Such an angular-velocity detection apparatus is disclosed in, for example, Japanese Unexamined Patent Publication (laid-open) No. 6-123632 (hereinafter referred to as "the prior art") is known.
An explanation of the prior art will now be given with reference to FIGS. 7 and 8.
In FIGS. 7 and 8, reference numeral 1 denotes an angular-velocity detection element of the prior art. Reference numeral 2 denotes a substrate formed in a rectangular shape, which forms the main body of the angular-velocity detection element 1, with the substrate 2 being formed of, for example, a high-resistance silicon material.
Reference numeral 3 denotes a movable section formed of low-resistance polysilicon, single-crystal silicon or the like having doped P, B, Sb or the like onto the substrate 2. The movable section 3 is formed of four support sections 4, 4, . . . provided on the substrate 2 so as to be positioned at the four corners of the substrate 2, four support beams 5, 5, . . . which are formed bent in the shape of the letter L in such a manner as to have a portion parallel to the X axis and a portion parallel to the Y axis from each support section 4 toward the central portion, and a rectangular vibrating body 6 which is supported by each support beam 5 in such a manner as to be capable of displacing in the X-axis and Y-axis directions and which is supported spacedly apart from the surface of the substrate 2. Electrodes 7 and 7 for vibration on the movable side, having provided therein a plurality of electrode plates 7A, 7A, . . . (four) in the shape of a comb, are protrusively provided on both siles of the left and right of the vibrating body 6, which is in the X-axis direction, and electrodes 8 and 8 for detection on the movable side, having provided therein a plurality of electrode plates 8A, 8A, . . . (four) in the shape of a comb, are protrusively provided on both siles of the front and back thereof, which is in the Y-axis direction.
In the movable section 3, only each support section 4 is fixedly secured to the substrate 2, and each support beam 5 and the vibrating body 6 are supported at four point in a state spaced apart by a predetermined amount from the substrate 2. Further, since each support beam 5 is formed in the shape of the letter L, by flexing the portion parallel to the Y axis, the vibrating body 6 can be displaced in the X-axis direction, and by flexing the portion parallel to the X axis, the vibrating body 6 can be displaced in the Y-axis direction.
Reference numerals 9 and 9 denote a pair of electrodes for vibration on the fixation side, provided on the substrate 2 in such a manner as to sandwich the vibrating body 6 from both sides of the right and left thereof. Each electrode 9 for vibration on the fixation side is formed of fixation sections 9A and 9A provided on the substrate 2 in such a manner as to be positioned on the right and left of the vibrating body 6, and four electrode plates 9B, 9B, . . . protrusively provided in the shape of a comb from each fixation section 9A in such a manner as to face with a gap each electrode plate 7A of the electrode 7 for vibration on the movable side.
Reference numerals 10 and 10 denote a pair of electrodes for detection on the fixation side, which are provided on the substrate 2 in such a manner as to sandwich the vibrating body 6 from both sides of the front and back thereof. Each electrode 10 for detection on the fixation side is formed of fixation sections 10A and 10A provided on the substrate 2 in such a manner as to be positioned on the front and back of the vibrating body 6, and four electrode plates 10B, 10B, . . . protrusively provided in the shape of a comb from each fixation section 10A in such a manner as to face with a gap each electrode plate 8A of the electrode 8 for detection on the movable side.
Reference numerals 11 and 11 denote vibration generation sections which serve as vibration generation means. Each vibration generation section 11 is formed of the electrode 7 for vibration on the movable side and the electrode 9 for vibration on the fixation side, with an equal gap being formed between each electrode plate 7A of the electrode 7 for vibration on the movable side and each electrode plate 9B of the electrode 9 for vibration on the fixation side. Here, if a driving signal of a frequency f at an opposite phase is applied between each electrode 7 for vibration on the movable side and each electrode 9 for vibration on the fixation side, an electrostatic attraction force is generated alternately between each electrode plate 7A and each electrode plate 9B positioned at left and between each electrode plate 7A and each electrode plate 9B positioned at right, and they come close to each other or move away from each other in each vibration generation section 11. This causes the vibrating body 6 to vibrate in the direction of the arrow a which is the X axis.
Reference numerals 12 and 12 denote displacement detection sections which serve as displacement detection means. Each displacement detection section 12 is formed of an electrode 8 for detection on the movable side and an electrode 10 for detection on the fixation side, with a facing length L0 being formed between each electrode plate 8A of the electrode 8 for detection on the movable side and each electrode plate 10B of the electrode 10 for detection on the fixation side. The electrodes 8 and 10 for detection are structured as parallel-plate capacitors for detection, and each displacement detection section 12 detects a change in the effective area between each electrode plate 8A and each electrode plate 10B as a change in the electrostatic capacitance.
In the angular-velocity detection element 1 structured as described above, if a driving signal of a frequency f at an opposite phase is applied to each vibration generation section 11, an electrostatic-attraction force alternately acts on the right and left vibration generation sections 11 and 11 between each electrode plate 7A and each electrode plate 9B, causing the vibrating body 6 to come close or move away in the direction of the arrow a and to vibrate.
In this state, when an angular velocity .OMEGA. about the Z axis is applied to the angular-velocity detection element 1, a Coriolis force (inertial force) is generated in the Y-axis direction, causing the vibrating body 6 to vibrate in the Y-axis direction by a Coriolis force F shown below at equation (2).
Here, a displacement x at which the vibrating body 6 is moved in the X-axis direction by each vibration generation section 11 and its velocity V are as in equation (1) below: EQU x=A sin(.omega.t) EQU V=A.omega. cos(.omega.t) (1)
where A is the amplitude of the vibrating body 6, .omega. is 2.pi.f, and f is the frequency of the driving signal.
Further, the Coriolis force F in the Y-axis direction generated from the angular velocity .OMEGA. applied about the Z axis when the vibrating body 6 is vibrated in the X-axis direction at a displacement x and velocity V is as in equation (2) below: ##EQU1##
Then, the vibrating body 6 is vibrated in the direction of the Y axis by the Coriolis force F of equation (2), and the vibration displacement by this vibrating body 6 is detected by each displacement detection section 12 as the change of the electrostatic capacitance between the electrode 8 for detection on the movable side and the electrode 10 for detection on the fixation side, making it possible to detect the angular velocity .OMEGA. about the Z axis.
Since each vibration generation section 11 is formed of the electrode 7 for vibration on the movable side formed of each electrode plate 7A and the electrode 9 for vibration on the fixation side formed of each electrode plate 9B, it is possible to secure a large effective area where the electrodes 7 and 9 for vibration face each other. As a result, when a driving signal is applied to each vibration generation section 11, an electrostatic attraction force generated between each electrode plate 7A and each electrode plate 9B is increased to vibrate the vibrating body 6 in the direction of the arrow a.
Meanwhile, since each displacement detection section 12 is formed of the electrode 8 for detection on the movable side formed of each electrode plate 8A and the electrode 10 for detection on the fixation side formed of each electrode plate 10B, it is possible to increase the effective area where the electrodes 8 and 10 for detection face each other. As a result, it is possible to detect the amount of the displacement of the vibrating body 6 which is displaced in the Y-axis direction by each displacement detection section 12 as a change in the effective area between each electrode plate 8A and each electrode plate 10B, i.e., a change in the electrostatic capacitance.
In the above-described angular-velocity detection element 1 of the prior art, the Coriolis force generated by the angular velocity .OMEGA. about the Z axis is very small, and therefore, it is necessary to generate a large displacement by using the resonance in the Y-axis direction. Meanwhile, to increase the Coriolis force, as even can be understood from equation (2), since the velocity V during vibration must be increased, a frequency near the resonance frequency in the X-axis direction is used as the frequency of the driving signal. Therefore, reaching a state close to the resonance frequency even at the vibration conditions in the Y-axis direction which serves as a detection axis is required to increase sensitivity.
However, if the resonance frequency in the detection direction is made to come close to the resonance frequency in the driving direction as described above, a part of the driving signal leaks (what is commonly called crosstalk) in the detection direction via the parasitic capacitance of the substrate 2 or the like. Then, this driving signal which leaked is applied to each displacement detection section 12, an electrostatic attraction force is generated between the electrode 8 for detection on the movable side and the electrode 10 for detection on the fixation side, and even in a state in which the angular velocity .OMEGA. does not act, vibration (hereinafter referred to as leakage vibration) appears in the vibrating body 6, presenting a problem of causing noise.